From sinapyl alcohol (s type monolignol) as a lignin-constituting component that is generated via phenylpropanoid synthesis pathway, syringin as s type monolignol glycoside is produced by glycosyl transferase (UDP-glucose transferase). In Arabidopsis thaliana as a model plant, there are about 100 kinds of glycosyl transferase, and it has been reported that, by forming glycosides of various compounds including plant hormones and secondary metabolites, they regulate the cellular activity and the storage of those compounds in a vacuole. Among them, UGT72E2 and UGT72E3 are reported as a glycosyl transferase responsible for converting firstly monolignol such as coniferyl alcohol and sinapyl alcohol specifically into monolignol-glycosides. Particularly, UGT72E3 as a sinapyl alcohol-specific glycosyl transferase required for syringin production has excellent substrate specificity for sinapyl alcohol, but its glycosyl transferase activity is so low that its application has been very limited. As such, development of a new glycosyl transferase useful for efficient production of syringin in a plant has been remained as a problem to be solved first before mass production and application of syringin, which is a pharmaceutically functional secondary metabolite.
Furthermore, for effective production of syringin in a plant via the phenylpropanoid synthesis pathway, it is also required to have a metabolic engineering technique which increase the content of sinapyl alcohol as a precursor of syringin that is present in a trace amount in a plant cell, as well as a strong glycosyl transferase activity having substrate specificity for sinapyl alcohol.
In particular, eleutheroside B (syringin) is classified as a representative adaptogen derived from plants, which is a pharmaceutical component from E. senticosus having excellent efficacy of psychological and physical adaptation against stress. The adaptogen is a terminology indicating a plant secondary metabolite which enhances non-specific resistance of a living body in response to various stresses without causing a side effect. Recently, syringin isolated in the pure state is reported to exhibit an excellent effect for diabetes and depression that become a serious problems of people living in modern-day cities, and thus its application is now broadened more than ever. However, because the area of cultivating E. senticosus is limited and there is a huge variation in pharmaceutical components depending on the area of cultivation, it is difficult to have the stable supply of E. senticosus required for production of syringin for commercial use. As such, development of a technique for stable production of a plant secondary metabolite like syringin, which is a highly valuable product, based on regulation of plant metabolic pathways using bioengineering techniques is needed.
Meanwhile, in Korean Patent Application Publication No. 2004-0004764, “Composition comprising extract of E. senticosus having hepato-protective activity or butyl alcohol soluble fraction thereof and butyl alcohol fraction of syringin and syringaresinol-di-O-β-D-glucopyranoside derivatives having anti-oxidant and hepato-protective activity” is disclosed. Further, in Korean Patent Application Publication No. 1998-0072707, “Pharmaceutical composition of syringin having liver function protecting activity” is disclosed. However, the method for producing a transgenic plant with increased syringin production and a plant obtained therefrom that are disclosed by the present invention have never been described before.